As known, a liquid crystal display (LCD) needs a backlight source for lighting up the frame of the LCD. The backlight source is a device which consumes the most power of the LCD. The power consumption of the LCD can be diminished by reducing the power consumption of the backlight source. A main rule of LCD circuit design is to diminish the power consumption of backlight source.
Referring to FIG. 1, a conventional DC to DC conversion circuit 10 comprises a DC power supply 102, a DC to DC converter 104, a power management IC 106, a load 108, a current feedback device 110 and two resistors R1, R2. The DC to DC converter 104 is capable of transferring a DC voltage provided by the DC power supply 102 to an output voltage Vout in order to supply the voltage needed by the load 108. The load 108 may be a backlight source of LCD. The backlight source can be consisted of a plurality of light emitting diodes (LED). The current feedback device 110 controls a current flowed through the load 108 in order to stabilize the current flowed through the load 108. The output voltage Vout is supplied to two resistors R1, R2 which are connected in series. The two resistors R1, R2 divide the output voltage Vout and provide a feedback voltage Vfb between the resistors R1, R2 to the power management IC 106. The power management IC 106 controls the DC to DC converter 104 to adjust the output voltage Vout in response to the feedback voltage Vfb so that the output voltage can be adjusted to meet the voltage needed by the load 108.
The series resistors R1, R2 are set with fixed resistances to match the voltage needed by the load 108. The output voltage Vout will still be a fixed voltage value when the voltage actually needed by the load 108 decreases. The feedback voltage Vfb divided by the series resistors R1, R2 will not be changed when the voltage actually needed by the load 108 decreases. Accordingly, the power management IC 106 can not control the DC to DC converter 104 to decrease the output voltage Vout. The higher output voltage will not only increase the power consumption of the load 108, but also decrease the durability of the load 108.
Therefore, there is a need to provide a novel DC to DC conversion circuit capable of reporting the variation of the voltage actually needed by the load to the power management IC for controlling the DC to DC converter to generate the voltage actually needed by the load. The novel DC to DC conversion circuit will not only capable of decreasing the power consumption of the load, but also capable of increasing the durability of the load.